Well cleaning with peracetic acid



Oct. 7, 1969 Filed Oct. 30. 1967 PERCETIC ACID ADDITION HYDROCHLORIC ACIDADDITION D. F. KREUZ 5TM- WELL CLEANING WITH PERACETIC ACID 2 Sheets-Sheet l 133i NI NOLLVAB'IB /'v\'/.'. /fl/-f` DONALD E KREUZ WILLIAM H. KIBBEL JR,

i Oct. 7, 1969 Q F KREUZ ETAL 3,470,959

I WELL CLEANING WITH PERACETIC ACID I lFiled Oct. 50. 1967 2 Sheets-Sheet .E

ELEVATION AFTER TERMINATING ADDITION OF WELL CLEANlNG AGENTS I I I 95 HYDROCHLORIC ACID -ELEVATION BEFORE HYDROCHLORIC ACID 90 TREATMENT ELEVATION IN FEET e5- ELEVATION BEFORE PERACETIC ACID TREATMENT PERACETIC ACID 75 I I l L l l O IO 2O 30 40 DAYS AFTER END OF CLEAN UP TREATMENT l`\`\"l;'\'lU/\'S DONALD F KREUZ WILLIAM H. KIBBEL JR,

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United States Patent O 3,470,959 WELL CLEANING WITH PERACETIC ACID Donald F. Kreuz, Princeton Junction, and William H.

Kibbel, Jr., Pennington, NJ., assignois to FMC Corporation, New York, N.Y., a corporation of Delaware Filed Oct. 30, 1967, Ser. No. 678,815 Int. Cl. E21b 43/27; C09k 3/00 U.S. Cl. 166-307 5 Claims ABSTRACT OF THE DISCLOSURE Seawater barrier, recharge wells, used to prevent seawater intrusion into underground potable water reserves, are cleaned and maintained free-flowing by adding peracetic acid into the wells with injected fresh water.

BACKGROUND OF 'THE INVENTION Field of the invention This invention relates to cleaning wells and more particularly to the cleaning of -wells into which fresh water is injected to prevent seawater intrusion into underground potable water source.

Description of the prior art In certain coastal areas, particularly certain sections of California, when fresh water is removed from underground sources, salt water commences to intrude into underground potable water basins. To prevent this contamination, a barrier has been formed by sinking a string of recharge wells 500 to 1,000 feet apart, parallel to the shoreline, and injecting fresh water therein. The injected water ows into the aquifer (underground earth formation) under a hydrostatic head of pressure fixed by the height of the water in the well above the aquifer. The ability of the well to accept water is measured most conveniently by determining the water elevation (height in feet f the Water column in the well above mean seawater levels) at a iixed water injection rate.

VOne problem that has arisen in this system is that after continuous use, the wells gradually become clogged and their capacity to accept water is seriously diminished. This is reflected by an increase in the required water elevation, that is, an increase in the height of the water column in the well, required to add water at a fixed water injection rate.

Various methods were attempted in an effort to remedy this problem. One includes the introduction of chlorine into the injected water at rates of from 1.5 to 12 mg./liter. In the absence of chlorinating the water, severe and rapid clogging attributed to bacterial growth may be obtained. However, it was found that the use of chlorine at residual levels of about 1.5-2 mg./liter of injected water is adequate for bacterial control within the aquifer adjacent the recharge wells, and that higher chlorination rates did not affect the more gradual, progressive type of Iwell clogging that occurred even when bacterial control was obtained by chlorination.

This progressive type of well clogging is most serious because it requires extensive redevelopment of the wells. Mechanical redevelopment techniques include (a) simple bailing land surging with a cable tool rig, (b) jet pumping and surging with an air lift, or (c) pumping and surging with a deep well turbine pump. In many cases the first two methods do not yield results and the third, more severe method, must be employed to reduce the well clogging. However, these methods are time consuming, expensive and require special rigs to carry out the well cleaning.

Chemical additives also have been used in an attempt to reduce well clogging. One such additive is hydrochloric 3,470,959 Patented Oct. 7, 1969 acid which is introduced into the injected water in amounts sufficient to lower the pH of the water to about 7. This reduces the tendency of the water to deposit mineral scale in the aquifer adjacent the recharge wells. The addition of hydrochloric acid appears to have a limited, beneficial effect, but the clogging resumes rapidly after the acid addition is stopped. In many cases, after suspending hydrochloric acid addition, the clogging resumes to a higher extent than previously to the acid addition.

OBJECTS OF THE INVENTION SUMMARY OF THE INVENTION It has now been found that the progressive clogging of seawater barrier, recharge wells, used to prevent seawater intrusion into underground potable water reserves, can be reduced by adding at least about 5 p.p.m. (and preferably from about 10 to about 1,000 p.p.m.) of peracetic acid to the water injected into the wells. Most surprisingly, the cleaning effect obtained by adding peracetic acid continues for an extended period even after use of peracetic acid is discontinued.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, FIGURE 1 illustrates, in graphic form, the effect of adding peracetic acid on the 'water elevation in the well; FIGURE 2 is similar except that hydrochloric acid was substituted lfor peracetic acid; FIGURE 3 cornpares, by graphic illustration, the water elevation in the wells after discontinuing the use of peracetic acid and hydrochloric acid.

DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS In carrying out the present invention, the peracetic acid must be injected into the recharge well. This is done most conveniently by pumping the peracetic acid at a controlled rate through an orifice placed in the well head. The pressure under which the peracetic acid is injected into the well head must be controlled in order to obtain uniform addition. The point in the water injection system where the peracetic acid is added is not critical and can be either at the well head or located in the water conduit leading to the well head. The peracetic acid is added to the injected water at any concentration at or above about 5 p.p.m. Concentrations of peracetic acid of from about 10 to 1,000 p.p.m. have been found most desirable and effective. However, concentrations of peracetic acid beyond this amount can be employed, 'although amounts larger than 1,000 p.p.m. do not yield any substantial improvement in the well-cleaning action.

The peracetic acid can be injected into the well either continuously or intermittently. If the acid is injected continuously, lower amounts of peracetic acid are injected into the well water on the order of 5 to 500 p.p.m. and the treatment is continued for a number of days. If intermittent addition of peracetic acid is used, higher concentrations of the peracetic acid on the order of 25 to 1,000 p.p.m. are injected for short durations of time. This latter intermittent type of addition has a shock elect on the recharge well and a more rapid drop in the water elevation (height of water column in the well) This rapid addition of peracetic acid or shock treatment can be carried out for several hours up to one full day, and then repeated as is necessary. In general, peracetic acid is added, whether by continuous treatment r intermittently, until the water elevation reaches its lowest point and continued additions of peracetic acid do not lower the elevation further.

The peracetic acid can be added at ambient temperature which may range from C. to 50 C. T'he temperature of addition is not critical except that temperatures above the boiling -point of peracetic acid should never be employed. For convenience sake the peracetic acid is normally added at the ambient temperature of the well site.

The concentration of the peracetic acid which is added can be at any concentration up to 100% peracetic acid. For convenience sake, the peracetic acid normally is added as 40% by weight peracetic acid, since this is commercially available and widely distributed.

The fresh water that is injected into the recharge wells is normally potable water. In order to insure potability of this injected water, it is common to chlorinate the water. The level of chlorination will vary depending upon the source of water, but normally chlorination providing a residual chlorine content on the order of 1.5-2 p.p.m. has been found effective in removing pathogenic organisms. The use of chlorine or other such bactericides normally used in rendering Water pathogenically free and potable does not interfere with the present use of peracetic acid in well cleaning.

In the present process, any additive which is introduced into the potable water supply as a well-cleaning agent must not leave toxic residues. Any toxic residues which remain after the additive has performed its well-cleaning function would be trapped in the aquifer and distributed to wells used to supply drinking water. In the present invention, peracetic acid, in addition to being an excellent well-cleaning agent, decomposes and yields as its residue, the innocuous substances, acetic acid and water. Peracetic acid also has an additional advantage in not being corro sive to the injection wells to any substantial extent, when used as set forth in the present invention. In addition, peracetic acid can be used under all pH conditions found in fresh Water supplies without requiring any adjustment of the pH in order to be effective.

The following examples are given to illustrate the invention and are not deemed to be limiting thereof.

Example I.-Process of the invention Run A-Shock treatment-One of a series of seawater barrier, recharge wells was used in the following test. It had a l2-inch, perforated, exterior, steel casing and a 4-inch, interior, plastic casing, gravel packed within the 12inch steel casing. Potable Water, chlorinated to a residual level of about 2 p.p.m. of chlorine, Was injected into the top of the casing at a rate of about 0.34 cu. ft./sec. The elevation of the water in the well prior to any treatment ranged from 83.8 to 85.1 feet. The elevation is defined as the height (in feet) of the water column in the well above mean seawater level for that area necessary to maintain a constant rate of water injection into the aquifer. A 250 pound barrel of 40% by weight peracetic acid was attached to the well head through a pump and tting in the well head. Plastic tubing 1A-inch in diameter was used to connect the well head fitting to the pump and to the barrel containing the peracetic acid. The 250 pounds of 40% by weight peracetic acid was added over a period of 18 hours and gave the well an initial shock elfect at a mean rate of 75 p.p.m. of 100% peracetic acid in the injected water. The rate of water injection was maintained at 0.34 cu. ft./sec. The elevation dropped to 74.3 feet. This data is set forth in Table I.

Run B-Continuous addition-After discontinuing peracetic addition for one day, the above well was treated by adding additional 40% by weight peracetic acid t0 the injected water at a rate sufficient to give 40 p.p.m. of peracetic acid in the injected water. Water injection was maintained at 0.34 cu. ft./sec. The peracetic acid was added for 17 days during which the elevation dropped from 74.2 to 69.5. The water elevation of the well also was recorded after addition of the peracetic acid was terminated to observe the long-range eiectiveness of the well cleaning. This 4data is also included in Table I.

TABLE I.-RECHARGE WELL CLEANING WITH PERA- CETIC ACID Elevation (feet) Remarks Days:

1 85. 1 No treatment. 2 85. l D0. 3 86. 0 D o. 4 85. l Do. 5. 83.8 Added 75 p.p.m. (100% basis o peracetic acid over 18 hours. 6. 74.3 Stop treatment. 7 73. 5 No treatment. 8. 74. 2 Restart 100 p.p.m. 40%, peracetic acid treatment. 9. 70. 6 Continue 100 p.p.m. 40%, peracetic acid treatment. 10- 69. 0 D0. 1l 69. 5 D0. 12. 69. 5 Do. 13- 69. 3 D0. 14. 69. 2 D0. 15 68. 8 D o. 16 70. 4 D 0. 17 70. 0 D 0. 18 70. 3 D o. 19 68. 8 D0. 20. 68. 8 D0. 21 68. 8 D 0. 22- 69. 6 Do. 23- 71. 0 Do. 24- 69. 5 Do. 25 70. 9 Stop treatment. 26- 70. 8 No treatment. 27 71. 7 Do. 28- 71. 7 Do. 29 72. 1 D0. 30 72. 6 D 0. 3l 72. 6 D0. 32 73. 1 D 0. 33 72. 6 D o. 34 72. 6 Do. 35 72. 0 D o. 36 72. 0 Do. 37 71. 9 D o. 38 71. 8 D 0. 39 71. 9 D0.` 40- 73. 9 Do. 41 71. 8 D0. 42. 71. 7 D0. 43. 71. 5 D0. 44- 71. 4 Do. 45 72. 9 D 0. 46- 73. 3 Do. 47 74. 4 D o. 48 73. 4 Do. 49 73. 7 D 0. 50 73. 9 D 0. 51 73. 9 D0. 52 74. 2 D 0. 53- 74. 2 Do. 54- 74. 2 D0. 55. 72. 4 D0. 56. 72. 6 D0. 57 74. 1 D o. 58- 74. 3 Do. 59 74. 4 D o. 60 74. 4 D 0. 61 7 2. 1 D 0. 62 73. 1 Do. 63 72. 2 D o. 64 72. 7 D o. 65-- 74. 3 Do.' 66. 71. 5 shutting well down:

Example A.Process of the prior art In order to demonstrate the effectiveness of peracetic acid over conventional additives, another example was 5 cient to alter the pH from its alkaline condition to a pH of 7.0. The rate of HC1 addition was altered depending on the pH of the incoming water to maintain a pH of 7.0. This addition was continued for 43 days after which the elevation was 78.7 feet. The water elevation was recorded after addition of the hydrochloric acid was terminated. This data is set forth in Table II.

TABLE IL-RECHARGE WELL CLEANING WITH HYDRO- CHLORIC ACID-Continued Water flow it/ Elevation, sec feet Remarks Days:

1 0.48 91. 0 No treatment. 2- 0.48 91. 0 Wtl pH adjusted from 8 to 7 with 3..- 0.53 67.4 DOJ 4.-- 0.53 66. DOJ 5.-- 0. 53 67. 5 DOJ 6-.- 0.50 67.0 DOJ 7..- 0.49 67.0 DOJ 8--. 0. 49 69.0 DoJ 9--.. 0.49 69.5 DOJ 10-- 0. 49 72.5 DOJ 11. 0. 49 75. 5 DOJ 12- 0. 49 76. 0 DOJ 13- 0.49 77. 5 DOJ 14. 0. 50 78. 0 DOJ 15.. 0. 50 78.6 DOJ 16.- 0. 51 73. 0 DOJ 17.. 0. 50 68.4 DOJ 18- 0. 50 69. 5 DOJ 19 0. 50 70.0 DOJ 20-- 0. 49 72.0 DOJ 21-- 0. 49 71. 7 DOJ 22.. 0. 49 71.6 DOJ 23.- 0. 49 72. 5 DOJ 24.- 0. 49 74.0 DOJ 25.- 0. 49 75.0 DOJ 26- 0. 49 75. 4 DOJ 27- 0. 49 75.4 DOJ 28. 0. 49 77.0 DOJ 29- 0. 49 77. 1 DOJ 30- 0. 49 76. 5 DOJ 31.- 0. 49 76. 6 DOJ 32- 0. 50 76. 5 DOJ 33- 0. 50 77. 5 DOJ 34. 0. 50 77.9 DOJ 35- 0. 50 77. 8 DOJ 36 0. 50 77.7 DOJ 37. 0. 50 77. 9 DOJ 38-- 0. 50 77. 9 DOJ 39.- 0.48 77.9 DOJ 40. 0. 51 78. 0 DOJ 4l- 0. 51 78.0 DOJ 42- 0. 51 78.4 DOJ 43.- 0. 51 78.6 DOJ 44. 0. 50 78. 7 DO.1 45 0. 50 78. 5 Stop HC1 addition. 46- 0. 50 82. 5 No treatment. 47-- 0. 50 85. 9 DO. 48. 0. 50 90. 5 D0. 49- 0. 50 91.0 DO. 50-- 0. 49 92. 0 D0. 51-- 0.49 92. 6 DO. 52- 0. 49 93. 5 D0. 53-- 0. 49 94. 0 Do. 54-- 0. 49 94.5 DO. 55-- 0.48 95. O D0. 56.- 0. 49 95. 9 Do. 57. 0. 49 95. 9 Do. 58- 0. 49 96. 3 Do. 59.- 0.51 96. DO. 60-- 0.50 96.5 D0. 61-- 0. 49 96.5 D0. 62- 0. 49 96. 5 DO.

1 Data on the quantity of HC1 required to adjust the pH varied.

Example II.-Process of the invention the elevation dropped markedly after shock treatment with peracetic acid as set forth in Run A; the elevation dropped further by subsequent, continuous addition as Set forth in Run B.

The changes in elevation resulting from hydrochloric acid addition as set forth in Example A are graphically illustrated in FIGURE 2. As will be seen from FIGURE 2, the hydrochloric acid addition also was eifective in reducing the elevation of the water in the well, but its effectiveness tapered off with continued hydrochloric acid treatment.

The changes in water elevation in the treated wells after terminating addition of peracetic acid and HC1 is set forth in FIGURE 3. As will be seen in FIGURE 3 the elevation of the water in the well treated with peracetic acid shows only a very slight perceptible rise 40 days after the end of the peracetic acid addition. However, the water elevation remains well below the original level that was present before addition of the peracetic acid. However, when hydrochloric acid treatment is terminated, in only 5 days the water elevation reached the original level that was present when hydrochloric acid addition was commenced. Thereafter, the water elevation climbed to 96.5 feet within 20 days which materially exceeds the water elevation which was present when HCl addition was begun. This indicates a return of the serious clogging problem. It is believed that this illustrates the unusual and unexpected long-range effect of peracetic acid as a well cleaner, and vis-a-vis hydrochloric acid.

Pursuant to the requirements of the patent statutes, the principle of this invention has been explained and exemplied in a manner so that it can be readily practiced by those skilled in the art, such exemplication including what is considered to represent the best embodiment of the invention. However, it should be clearly understood that, within the scope of the appended claims, the invention may be practiced by those skilled in the art, and having the benet of this disclosure otherwise than as specifically described and exemplified herein.

What is claimed is:

1. In the process of preventing seawater intrusion into underground water reserves wherein fresh water is injected into seawater barrier, recharge wells and wherein said recharge wells become gradually clogged with continued use, the improvement which comprises adding at least about 5 p.p.m. of peracetic acid to said water injected into said wells whereby said clogging is reduced.

2. Process of claim 1 wherein said peracetic acid is added in amounts of from l0 to 1,000 p.p.m.

3. Process of claim 1 wherein said injected water is sanitized, potable water.

4. Process of claim I wherein said peracetic acid is added continuously at a rate of 5 to 500 p.p.m.

5. Process of claim I wherein said peracetic acid is added intermittently at a rate of about 25 to 1,000 p.p.m.

References Cited UNITED STATES PATENTS 2,590,856 4/1952 Greenspan et al 167-22 3,152,640 10/1964 Marx 166-42 X 3,202,215 8/ 1965 Stanonis 166-42 3,329,610 7/1967 Kreuz et al. 166-9 X STEPHEN I. NOVOSAD, Primary Examiner U.S. Cl. X.R. 252-855 

